You need a tweak to the launcher to force usage of GTK2 instead of GTK3.
Either create a wrapper script like this

#!/bin/bash
export SWT_GTK3=0
$STUDIO_HOME/./devstudio

or edit
$STUDIO_HOME/studio/devstudio.ini
and add

--launcher.GTK_version
2

at the very beginning of the file

Install teiid Designer

In the Red Hat Central window in the center, click the Software/Update tab at the bottom

Check the box next to JBoss Data Virtualization Development

Click the Install/Update button to install the teiid designer

If you do not see JBoss Data Virtualization Development listed, check the Enable Early Access checkbox in the lower right. Sometimes the teiid designer release does not sync with the JBDS release.

After installation, restart JBDS. On reboot you will be asked for a secure storage password, you can choose something simple like redhat

Configure the server settings

Click the green arrow in the bottom of the server tab to start the server.

It is recommended to start the JDV outside of the designer to keep the server running between designer restarts. If you start the server outside the designer you will receive a prompt to Mark the server as started. This is fine.

Then double-click the server name and go to the teiid instance tab

Click test the administration connection and check for ok

Enter the jdbc connection username of teiidUser with the password from installation, Password1!

Click Test the JDBC connection and check for ok

Finally, save the changes by clicking the disk icon in the upper left or ctrl+s